This invention relates to zig zag sewing machines and, more particularly, to sewing machines having the capability of automatically producing buttonholes of various sizes.
Many different types of automatic buttonhole mechanisms are presently in use on sewing machines, both cam controlled and electronically controlled. These mechanisms typically require a special presser device for holding the work. Such presser device also commonly includes an arrangement whereby the length of the buttonhole pattern is defined by a gauging element which is moved in accordance with the size of the button for which the buttonhole pattern is being sewn. A number of different arrangements have been proposed in the past for sensing the desired buttonhole pattern length. For example, U.S. Pat. No. 4,056,070, discloses an arrangement wherein conductive markers are placed on the work at the top and bottom of the desired buttonhole location. The presser device contains electrical contacts and the conductive markers complete a circuit when the contacts ride over the markers. Another exemplary arrangement is disclosed in U.S. Pat. No. 4,159,685, wherein a presser device includes a fixed stop member and an adjustable stop member, the distance therebetween defining the length of the buttonhole pattern being sewn, as determined by the size of button inserted between an anchor element and a button gauging element. The sewing machine includes a switch mechanism including a lever arm terminating in a paddle at its lower end. The lever arm is selectively raised and lowered by an operator, the operator lowering the lever arm so that the paddle is between the stops during the formation of a buttonhole pattern. At the upper end of the lever arm, opposite the paddle, and within the head of the sewing machine, is a switch assembly which is actuated when the stops ride up against the paddle. A third exemplary arrangement is illustrated in U.S. Pat. No. 4,216,732, which discloses an optical buttonhole switching arrangement in which the movements of reflective areas carried on a movable buttonhole foot are sensed. The spacing of the reflective areas is adjustable to accommodate buttons of different sizes.
While generally satisfactory, such devices are susceptible to false operation resulting from improper setting up by the operator or due to the operator manipulating the fabric in the vicinity of the presser device.
Additionally, when using a paddle device, it is also possible to bend the paddle out of position.
It is therefore an object of the present invention to provide a buttonhole presser device which is easy to use and which has a greatly reduced susceptibility to false operation.